1. Field of the Invention
This invention relates to ophthalmological devices, and more specifically to a new sterile cover for the prism of an applanation tonometer or a similar device and, a packaging device for the sterile cover. Further, the invention relates to a method of mounting the cover onto the prism without human contact with the sterile area and of dismounting the cover from the prism without human contact with the area of the cover that has potentially been exposed to infectious disease microorganisms.
2. Disclosure of the Prior Art
The invention hereof is discussed within the bounds of the medical technology surrounding the Goldmann applanation tonometer, the technic for using the same, and the medical literature arising from the application thereof. The Goldmann applanation tonometer is an ophthalmological instrument, described in U.S. Pat. No. 3,070,997 to Papritz, Goldmann and Schmidt and assigned to Haag-Streit AG, Bern, Switzerland. The instrument is principally manufactured by the assignee whose product literature entitled, "Goldmann Applanation Tonometer Model T900, R900, 1080 and 870" is further descriptive of the present-day technology and thereby provides a background against which the present invention can be more readily understood.
The need for new sterile ophthalmic technics has been urged in recent years as the understanding has grown of the communicable nature of viral and bacterial infections. Few practicing opthalmologists have not at sometime been unfortunate enough to have a patient return to their office with an eye infection which was likely contracted during a previous examination. Even in an office where meticulous hand washing and other good hygiene rules are maintained, patients are still at risk for contracting an infectious disease. In ophthalmic practice, it is believed that communication of infectious disease is likely to occur during applanation tonometry as the tonometer prism is the only instrument that comes into direct contact with the patient's eye during a routine examination. Medical literature has documented the presence of various viruses on tomometer prisms including adenovirus type 8, herpes simplex virus type 1 and hepatitis B surface antigen. Refer to Craven et al, "Applanation tonometer tip sterilization for adenovirus type 8, Opthalmology 1987; Ventura et al, "Viability of herpes simplex virus type 1 on the applanation tonometer," American Journal of Opthalmology (AJO) 103:48, 1987; and, Moniz et al, "Removal of hepatitis B surface antigen from a contaminated applanation tonometer," AJO, 91:522-525, 1981.
The rising incidence of the Acquired Immune Deficiency Syndrome (AIDS), has stimulated much renewed concern regarding the spread of infection by applanation tonometry. AIDS has been found to be caused by the human immunodeficiency virus (HIV) which was previously thought to be transmitted only by sexual and direct intravenous routes. However, a recent report describes an AIDS laboratory worker showing positive HIV serology with no history of these risk factors To date there have been no reported studies of HIV and tonometer prisms or cases of AIDS being transmitted via applanation tonometry. However, this theoretical possibility does exist as HIV has been isolated from human tears, corneal tissue and conjunctival epithelium. Of greatest concern is the recent evidence indicating that AIDS can be contracted by exposure of intact mucous membranes such as the lips and mouth to the virus. This raises the distinct probability that AIDS could be communicated from one patient to another by applanation tonometry. Refer to Schuman et al, "Acquired immunodeficiency syndrome (AIDS)," Survey of Ophthalmology 31:384-410, 1987; Fujikawa et al, "Isolation of human T-cell leukemia/lymphotopic virus type III (HTVBL-III) from the tears of a patient with acquired immunodeficiency syndrom," Lancet 2:529-530, 1985; Salahuddin SA, et al, "Isolation of the human T-cell leukemia/lympotropic virus type III from the cornea," AJO 101:149-152, 1986; and, Fujikawa et al, "Human T0cell leukemia/lymphotropic virus type III in the conjunctival epithelium of a patient with AIDS," AJO 100:507-509, 1985.
Various methods have been utilized in the past to reduce the risk of transmitting infectious disease via applanation tonometry. These range from wiping the prism with various substances to removing the prism and storing it in a disinfecting solution. Although some of these methods have, when used correctly, been shown to sterilize effectively the tonometer prism, several shortcomings are still present which prevent these methods from providing the optimal solution. To sterilize the tonometer prism effectively by wiping the prism while still in its holder with a disinfectant solution precludes the minimum 5 minute disinfectant exposure recommended by the Center for Infectious Diseases in Atlanta (refer to: Morbidity & Mortality Weekly Report, 34:533-4, 1985).
Unless all disinfectant is removed from the tonometer surface prior to measuring intraocular pressure, the residual disinfectant will cause toxic corneal epithelial damage. Removal of disinfectant requires rinsing the prism with sterile saline or water. Additionally, according to the manufacturer, damage to tonometer prisms may result from application of alcohol. Furthermore, repeated mechanical cleaning reduces the smoothness of the prism; such small scratches and pits may shield microorganisms from the disinfectant. Moreover, they reduce the accuracy of the instrument. Sterilization technics requiring removal of the tonometer prism from its holder, while superior in terms of disinfection are less convenient and therefore less likely to be employed in a busy office setting. These technics require removal of the prism, placement in a container which may contain a substance toxic to the skin and a wait of 5-10 minutes for adequate disinfection. The prism is then stored. Corboy et al reports that Shapiro has suggested wrapping the prism in transparent strips of plastic household film. The prism must then be rinsed in sterile saline or water and dried before being reinserted into the prism holder. If this system is employed, more than one prism must be on hand to rotate through the system. Also, unless sterile gloves and a sterile drying cloth are used the potential exists for re-contamination while inserting the prism back into its holder. Refer to Corboy et al, "Mechanical sterilization of the applanation tonometer," AJO, 71:889-91, 1971.
With these prior art methods, direct contact between the tonometer prism and the precorneal tear film is still necessary to measure accurately the intraocular pressure. As a result of the direct contract, the possibility always exists for contamination, especially as no mechanical barrier to infectious microorganisms has been employed.